Mechanical stress is the dominant factor in activation of bone remodeling, but the mechanism of its action on osteoblasts is largely unknown. The goal of this once-revised R01 application is to study molecular mechanisms involved in transduction of mechanical stress in bone to a biological response in osteoblasts. This study will employ an in vivo model of transgenic mice to analyze transcriptional regulation of the alpha 1(1) collagen (COL1A1) gene in bone cells under mechanical stress. The periodontium of transgenic mice, harboring the COL1A1 promoter directing the expression of a reporter gene (CAT), will be mechanically stressed by applying a defined and reproducible force on the maxillary first molar. Preliminary data from the applicant's laboratory, showed that periodontal osteoblasts respond to mechanical stress in a cell-specific manner by an enhancement of COL1A1 gene expression. Based on these results, the objective of these studies is to define regulatory regions of the COL1A1 promotor, which mediates the mechanical response. Using the peak response of the COL1A1 gene, the first goal will be to identify a chimeric promoter construct (starting with the 3.6 kb fragment) that responds similarly to the endogenous COL1A1 gene. The identified fragment will then be used to accomplish the final goal, which is to map the regulatory region of the COL1A1 promoter that mediates the mechanical response. Constructs containing progressively smaller fragments of the COL1A1 promoter will be tested to localize DNA regulatory elements and binding sites for nuclear transcription factors involved in the osteoblast response. Once a smaller promoter fragment of about 200 nucleotides is identified, its mechanically-induced interactions with nuclear transcription factors will be analyzed by gel mobility shift assay, and further delineate a minimum promoter sequence which mediates the response to mechanical stress. This approach will indicate whether the pathway for transduction of a mechanical signal is similar to, or distinct from, pathways used by known growth factors and hormones that modulate type 1 collagen production in osteoblasts.